| Abstract: | The Mohr-Coulomb criterion needs to be modified for highly anisotropic rock material and jointed rock masses. Taking σ2 into account, a new strength criterion is suggested because both σ2 and σ3 would contribute to the normal stress on the existing plane of weakness. This criterion explains the enhancement of strength (σ2 – σ3) in the underground openings because σ2 along the tunnel axis is not relaxed significantly. Another cause of strength enhancement is less reduction in the mass modulus in tunnels due to constrained dilatancy. Empirical correlations obtained from data from block shear tests and uniaxial jacking tests have been suggested to estimate new strength parameters. A correlation for the tensile strength of the rock mass is presented. Finally, Hoek and Brown theory is extended to account for σ2. A common strength criterion for both supported underground openings and rock slopes is suggested. |
